A doomed love story, especially one based on real-life young people braving their own “The Fault in Our Stars”-style tale, is bound to shatter even the coldest of hearts. Earnest, disarming and unapologetically conventional, prolific graphic artist Phuong Mai Nguyen ’s elegantly animated feature debut “ In Waves ” grasps this fact on such a philosophical level that it aims to do not a great deal more than wash over the viewer with its raw sentiments. Right out of the gate, you can see a soft-hearted tearjerker on approach like a rolling wave, one that will inevitably swell in size and break at the exact spot that you’ve been standing. And you might as well let it do exactly that. “In Waves” offers viewers a good old-fashioned cry, in the form of a traditional emotional rollercoaster that wants to win over our cynical hearts in hordes.…